Fusion as an Opportunity for Calorimetrically Probing Polymer Conformations and Interactions in the Bulk State

Abstract

It is a well documented1 fact that the fusion or melting of crystalline polymers is a first-order phase transition “between two polymeric states in equilibrium: the crystalline and molten amorphous, or liquid states. Consequently, the melting temperature Tm is well defined and given by

where ΔH and ΔS are the differences between the enthalpy and entropy, respectively, of the crystalline and molten polymer phases in equilibrium at T. Unlike calorimetric studies of the glass transition in polymers, for example, whose interpretations in terms of polymer chain conformations and interactions suffer from a lack of knowledge of the state of the polymer chains both above and below this transition, because the polymer chains may not be in equilibrium, 2 the fusion process affords an opportunity for studying the effect of molecular structure on the melting temperature and, more importantly, upon both components of the ratio ΔHu/ΔSu which determine Tm.